Polyoxyalkylene ethers of citric acid



United States Patent 3,278,593 POLYOXYALKYLENE ETHERS 0F CITRIC ACID George P. Touey and Herman E. Davis, Kingsport, Tenn.,

assignors to Eastman Kodak Company, Rochester, N.Y., a corporation of New Jersey No Drawing. Filed July 21, 1965, Ser. No. 473,817

4 Claims. (Cl. 260-535) This application is a continuation-in-part of application Serial No. 170,526, filed February 1, 1962, now abandoned.

This invention relates to a new type of oil soluble citric acid derivative useful as a metal deactivator and more particularly to polyoxyalkylene ethers of citric acid which are soluble metal deactivators for edible fats and oils and for petroleum products.

Many organic materials, such as gasoline, lubricating oils, rubber, and edible fats and oils, are subject to oxidative deterioration during contact with air. Such oxidation is undesirable and generally renders the material unfit for its intended use. Thus, gasolines become gummy, lubricating oils thicken and become acidic and fats become rancid. Oxidation is accelerated by a rise in temperature, by the action of sunlight and the catalytic effect of certain metals such as copper, cobalt and manganese.

The above-mentioned metals are harmful, either in the solid metallic form or as dissolved organic compounds such as acid salts. Only trace amount (1 p.p.m.) of a copper salt, such as cu-pric oleate, for example, can greatly reduce oxidation stability. Salts can occur naturally in the materialor through the action of small amounts of organic or inorganic acids present in the material on coppercontaining equipment used to process, store or utilize the material. Thus, gasoline may be contaminated with cop-v per as a result of the refining process or may acquire a certain small amount of the metal in use, as by passage through pumps and lines constructed of copperv alloys or through copper or copper-lined fuel lines and carburetors.

Avoidance of copper is thus often impractical or impossible. A widely used remedy is to employ a copper (or other metal) deactivator which will tie up the metal in an inactive form in which it is no longer able to function as an oxidation catalyst. Many types of organic molecules can. act as such' metal deactivators. For any specific application, however, the deactivator must be selected to meet'the particular requirements of such an agent,1s'uch as efiiciency, solubility, non-toxicity, compatibility, non-extractibility (such as by water) and reasonable cost. Generally deactivators contain several groups such as phenolic OH,COOH, NH NHR, SH, -'-SR, etc. A typical metal deactivator is N,N'- disalicylidene-l,2-propylenediamine. Its union with copper'ion is shown below:

on oil H0 Thus, for example, in using citric acid as a metal deactivator in lard a large proportion of propylene glycol is normally used as a co-solvent for the acid. Even with "ice such oo-solvents there is always the possibility that the citric acid will crystallize out of the final product and hence become ineffective to remove metallic ions.

One method for rendering citric acid more soluble in fats, oils, gasolines and the like is to esterify one of its three free carboxyl groups with a long chain aliphatic acid. Pertinent information on the citric acid ester type of metal deactivators has been reported in such US. patents as 2,701,203 and 2,686,751 and in the literature, for example, Food Technology, 8, pp. 6-9 (1954) and J. Amer. Oil Chemist Soc., 32, pp. -176 (1955). Although such methods as those disclosed for solubilizing citric acids are useful they have one obvious disadvantage. This is the blocking of one of the active carboxyl groups in the product by the formation of an ester group. It is well known to the art that citric acid owes its metal deactivating power to the presence of its three carboxyl groups. Therefore, any derivative of the acid which would have less than three carboxyl groups available would have a reduced activity toward metal ions. In fact, it has been reported [Food Technology, 8, pp. 6-9 (1954)] that diand triesters are completely inactive as metal deactivators.

This invention has as an object to provide a new and improved process for deactivating metal ions present in substances such as edible fats and oils and in petroleum products such as gasoline and lubricating oils.

This invention has as another object to provide a new class of metal deactivators for the treatment of edible fats and oils and petroleum products such as gasoline and lubricating oils.

A further object is to provide a citric acid-derived metal deactivator which contains in its molecule three free carboxyl groups capable of combining with metal ions.

A further object is to provide a citric acid-derived metal deactivator which is soluble in edible fats and oils and in gasoline and lubricating oils.

Other objects will appear hereinafter.

These objects are accomplished by the following invention which is based upon the broad concept of altering the citric acid molecule so as to provide a derivative which is soluble in those organic substances from which it is desired to remove metal ions and at the same time will have the three carboxyl groups of the citric acid molecule preserved intact and available to function to tie up the metal ions present in the substance undergoing treatment as, for example, -a gasoline or lubricating oil or an edible fat or oil. Specifically, the new metal deactivators of our invention are polyoxyalkylene ethers of citric acid having the structural formula indicated below:

homolog, namely the polyoxyethylene ether of citric acid,

was found to be essentially inoperative in practicing the invention. This appears to be due to the fact that the oxyethlene groups as they are present in the structural formula above are not oil soluble and are therefore not useful in.

making the citric acid derivative soluble in edible fats,

edible oils, gasoline or lubricating oils. On the other hand, oxypropylene and oxybutylene groups are oil soluble and water insoluble, thus making them ideally suitable for making a citric acid derivative soluble in edible fats, edible oils, gasoline or lubricating oils. No known basis exists for explaining the results which can be obtained when such groups are present as constituent structural elements of various derivatives, hence the preceding theoretical discussion should not be construed as imposing any limitations with respect to the unexpectedly advantageous discovery embodied in the present invention.

The formation of such ethers is illustrated by the following equation for the preparation of an ether which may be identified as tripolyoxypropylene ether of citric acid:

CHgCOOOHgCHa BF 3 HO- O O O CHZCHg 3OH -CH-OH OH OOOCH2OH;;

OH; OH; CH CH2COOCH2OH3 HO-HCHzO- HCHzO( JH-CHzO C O O OHzCH;

lNaOH nzooocnlom CH (llH CH CHzCOONa HO-OH-OH O-CHOH O( JHOHzO COONa 3CH GH OH l n20 OONa a on CH ona c1120 0 OH HO(] H-OI-IzO-JJ HCH2O( JHCH2O C O OH H 0 0 OH (Tripolyoxypropylene ether of citric acid) It will be evident that in these polyoxyalkylene ethers of citric acid the three carboxyl groups of the citric acid molecule have been preserved intact and are thus available to tie up the metal in the substance undergoing treatment such as, for example, an edible oil or fat. Such compounds are soluble in and thus compatible with such products as edible oils and fats as well as gasoline and lubricating oils by virtue of the presence in the molecule of the polyoxyalkylene ether group. We have found that such compounds have a sufiicient solubility in such substances as to be sufliciently dispersible or soluble therein to uniformly pick up the metallic ions it is desired to deactivate. It will at course be understood by those skilled in the art that the solubilities of the citric acid ether derivatives when employed as metal deactivators in accordance with our invention will vary in their solubility with respect to any given substance. For example, in some instances the polyoxyalkylene ethers of citric acid of our invention will be soluble in corn oil to the extent of approximately 50 percent, while in lard the solubility,

depending on the temperature, may be only 3 percent and in gasoline and lubricating oil only about 1 percent. However, even in the case of the lower solubilities we have found that these citric acid ether derivatives are valuable as metal deactivators.

In treating edible fats and oils as well as gasoline and lubricating oils with the above-mentioned citric acid either derivatives the compound is simply added to the substance undergoing treatment and thoroughly mixed therein in the desired amount, which, in any event, will be at least equivalent to the amount of metal ion content to be removed. This in most cases will range, for example, from 0.0001 to 0.5 percent by weight of the substance undergoing treatment. The actual amount used in any given instance will of course vary widely, depending, not only upon the specific nature of the material itself, but also upon the source from which it was derived. For example, an edible fat such as lard derived from one source may contain only a moderate amount of metal ions, while another sample of lard derived from another source may have a much higher concentration of contaminating metal present there and will therefore require a proportionately larger amount of the citric acid ether derivative above described to deactivate the metal ion component.

The metal containants which are generally met with inedible fats and oils as well as in gasoline and lubricating oils, are copper, cobalt, iron, nickel and manganese although other metal contaminants may also be present. We have found that the citric acid ethers herein described are useful as metal deactivators for these and other metals but have been found especially effective in deactivating the copper found to be present in certain edible fats an fat such as lard which has been treated with a citric acid ether derivative of our invention to deactivate the metal ion contaminant the so-called Active Oxygen Method described in Oil and Soap 20, pp. 169-171 (1943), also in US. Patent 2,739,066 may be employed. In the case of gasoline the so-called Oxygen Bomb Stability Test described in Industrial Engineering Chemistry (Ind. Ed.), 24, p. 1375 (1932) may be employed to evaluate the effectiveness of the metal deactivators of the present invention when employed in the treatment of this type of material.

In the following examples and description we have set forth several of the preferred embodiments of our, invention but they are included merely for purposes of illustration and not as a limitation thereof.

The citric acid ether derivative deactivators of our invention may be prepared as disclosed in the following typical example illustrating one embodiment of the invention.

Example 1.-Preparation 0 polyoxypropylene ether of citric acid Eight moles (464 g.) of propylene oxide was slowly added over a 3 hour period to a stirred mixture of 0.1.

dium bicarbonate and then washed with water. Theethereal solution was dried and the ether flushed off. The residue was heated to a pot temperature of 180 C. at 1 mm. pressure to remove any unreacted triethyl citrate as Well as any propylene glycol. The viscous residue was dissolved inl liter of an ethanol )water (10%) solution containing 3 moles (16 8 g.) of KOH. The solution was refluxed for 2 hours to completely saponify the ether ester. The ethanol and'water were removed by distillation and the residue extracted with ethyl ether to remove any polypropylene glycol. The residue was made strongly acidic with hydrochloric acid and extracted continuously with ethyl ether for 48 hours. The ether extract was then concentrated under reduced pressure to give the polyoxypropylene ether of citric acid, a viscous yellow liquid with the following structure:

The neutral equivalent of the product was about 134-137, indicating that the product contained an average of 4 propylene oxide condensation units, i.e. the average value p of x was 4. The product was soluble in such products as lard, corn oil, cotton seed oil and peanut oil, as well as in petroleum products such as gasoline and lubricat ing oils. It was soluble in the common aliphatic and aromatic organic solvents, such as acetone, ethanol, dichloromethane, ethyl ether, propylene glycol, benzene, toluene, xylene. -In water, however, the product was essentially insoluble.

Example 2.Preparation of polyoxybutylene ether of citric acid Eight moles (576 g.) of butylene oxide (mixture of It was Example 3.U se 0f polyoxyalkylene ethers of citric acid as metal deactivating agents for iron in an edible fat The polyoxypropylene ether of citric acid designated in the table below as PECA and the polyoxybutylene ether of citric acid designated as BECA were tested as metal deactivating or chelating agents when such agents were used to treat a commercial lard (stabilized with butylated hydroxyaninsole (BHA as an antioxidant) employing the above-identified Active Oxygen Method for the evaluation. As is known to those skilled in the art to which this invention relates, thisvtest involves bubbling air through the lard sample at a temperature of 99 C. whereby peroxides are formed and the oxidation is 01- lowed,by a determination of milliequivalents of such peroxides per kilogram of substrate. oxide'value of 20 is the upper limit which can be tolerated in edible fats, for example. Above this value fats exhibit an objectional degree of rancidity.

In carrying ou the above-mentioned test a stabilized sample of lard containing 0.01% BHA and 1 p.p.m. iron was prepared as follows: a 0.01 g. sample of BHA was added to 99.99 g. of lard along with 1 ml. of an ethanol solution of ferric oleate so that the resulting solution or mixture contained 1 part per mil-lion of iron as ferric ion. This mixture was placed on a steam bath heated to about 78 C. and stirred continuously for 25 minutes during which time the ethanol was removed from the mixture by evaporation. 20 ml. of the stabilized lard solution was placed in an A.O.M. tube maintained at 99 C. and air bubbled through at a rate of approximately 2.3 nil. per second. Periodically, a portion of the test solution was removed and the peroxide content quantitatively determined by iodametric titration, the results being expressed as milliequivalents per kilogram of sample. A control containing no additive was run simultaneously to determine the induction period of the unstabilized material. The final results are expressed as the number of hours required for rancidity to develop; i.e., an A.O.M. value of 20 for the sample, meaning that 20 hours was required to form 20 milliequivalents of perxoide per kilogram of the lard sample. Such a test is described in US. Patent to Tholstrup et al. No. 2,739,066. The effectiveness of the citric acid ether derivatives of our invention in controlling or eliminating the oxidative efiect of metal ions in lard, a typical edible fat, is clearly shown in Table 1 below:

6 TABLE 1 Efiect of PECA and BECA as deactivators for iron Sample: A.O.M. value Lard, control (not deactivator norm metal contaminant) 4 Lard+1 p.p.m. iron (added as ferric oleate) 0.5 Lard+0.01% BHA 18 Lard+0.01% BHA+1 p.p.m.'iron 3 Lard+0.0l% BHA+1 p.p.m. iron+0.0%

PECA 20 Lard+0.01% BHA+1 p.p.m. iron+0.05% BECA 19.

The deleterious effect of iron is demonstrated in this table and the metal deactivating eifectiveness of the POIYOXY'. propylene ether of citric acid and of polyoxybutylene ether of citric' acid of our invention is clearly shown. Thus, lard containing these agents and iron have substantially the same stability as lard stabilized with BHA in the absence of such metal contaminants.

Example 4.-*P0ly0xyalkylene ethers of citric acid as metal deactivating agents for copper in an edible fat Samples of lard were prepared as in Example 3 and tests were carried out using the same procedure as in that example, the BHA and metal decativator being weighed out and mixed with the lard prior to test. The results obtained are indicated in Table 2 below:

TABLE 2 Eflect 0f PECA and BECA as deactivators for copper Sample: A.O.M. value Lard, control l0 Lard+1 p.p.m. copper (added as cupric chloride) 1 Lard+0.01% BHA Lard +0.01% BHA+1 p.p.m. copper 1 Lard+'0.01% BHA+.1 p.p.m. copper+0.05%

PECA 40 Lard+0.01% BHA+1 p.p.m. copper+0.05%

I. BECA" 43 Ordinarily, a per- Example 5 .P0ly0xyalkylene ether of citric acid as metal deactivators in gasoline The test medium in this case consisted of a Pennsylvania cracked gasoline. In order to determine the efiectiveness of the polyoxya-lkylene' ethers of our invention as metal deactivators samples were prepared by adding an amount of metal to each sample corresponding to 1 mg. of metal per liter of gasoline. To each sample, except the control, was added 0.0096 weight percent of p-butyl-n-aminophenol as an antioxidant. 0.003 weight percent of polyoxyalkylene ether was added to samples it was desired to test for deactivating elfect. Each of the samples, including the control sample, was then subjected to the above-mentioned Oxygen Bomb Stability Test described in Industrial and Engineering Chemistry (Ind. Ed), 24, p. 1375 (1932). This test measures the induction period of the gasoline, or length of time in minutes before rapid oxidation of the gasoline begins. In carrying out the test, a 200 ml. sample of the gasoline in a glass bottle is heated to 21.1.6" F. at lbs/sq. in. oxygen pressure in a stainless steel bomb. The bomb is connected to a pressure recorder, which indicates a sharp drop in the pressure curve at the end of the induction period. The induction period may be defined as the time in minutes elapsed from the beginning of the test to the time at which a rapid decrease in oxygen pressure occurs.

The pro-oxidant effect of metals in gasoline, as well as the etfectiveness of the polyoxyalkylene ethers of our invention in deactivating these metals, is shown in the Table 3 below. The increased stability imparted by the addition of these ethers to the metal-containing gasoline is clearly indicated.

TABLE 3 Efiect of PECA andBECA as metal deactivators in gasoline Antioxidant (p-Butyl- Metal Present, BECA PECA Induction amino-phcnol Ooncen- 1 mg./Liter Concentration, Concentration, Period,

tration, wt. percent wt. percent Wt. percent minutes None None 95 0. 0096 .do 490 0. 0096 -do 130 0. 0096 0. 003 435 0. 0096 450 0.0096 None 365 0. 0096 0. 003 565 0. 0096 540 0. 0096 None 405 0. 0096 0. 003 495 0. 0096 510 1 As copper oleate. 2 As cohaltous oleate. 3 As manganous oleate.

three carboxyl groups of the citric acid molecule are avail able for deactivating action and by the fact that the polyonyalkylene ether group renders the compound soluble in a wide variety of aromatic [and aliphatic solvents and thus renders them particularly applicable to the metal deactivating treatment of edible fats and oils and petroleum products. 7

Although the invention has been described in detail with particularreference to certain preferred embodiments thereof,-variations and modifications can be eifected within the spirit and scope of the invention as described hereinabove and as defined in the appended claims.

We claim:

1. Po1yoxyalkylene ethers, of citric acid having the structural formula:

nwmroil-ooon i HzCOOH I wherein R is a member selected from the group consisting of propylene and butylene and x has an average value wherein R is a member selected from the group consisting' of propylene and butylene and x has an average value of x is about 3 and R is propylene.

4. The compound of claim 2 wherein the average value of x is about 3 and R is butylene.

References Cited by the Examiner LORRAINE A. WEINBERGER, Primary Examiner.

A. P. HALLUIN, Assistant Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,278,593 October 11, 1966 George P. Touey et al.

rror appears in the above numbered pat- It is hereby certified that e said Letters Patent should read as ent requiring correction and that the corrected below.

strike out "when,"; column 4, line 12,

Column 1 11116 67,

tor "COHKELHaHKS" read contaminants column 5, line 46, for "on" 1 ead I out line 68 for "perxoide" read peroxide column 6, line 5, for "(not deactivator norm" read {no deactlvntor nor column 6, line 10, for

"O 0%" read 0 .O5%

Signed and sealed this 26th day of September 1967.

(SEAL) Attest:

EDWARD J.

ERNEST W. SWIDER Commissioner of Patents Attesting Officer 

1. POLYOXYALKYLENE ETHERS OF CITRIC ACID HAVING THE STRUCTURAL FORMULA: 